Timing by Vacuum Reading?
The vacuum gauge is used to adjust the carbs air/fuel mixture. Set the initial timing to whatever the engine will take and still start without lugging the engine down.
Curves and total timing are another thing. As you said a non stock engine has no book specs. If it pings, back off on the timing.
Making a/f and timing adjustments on non stock engines often requires someone who has experience with a similar set-up. Can't really be done on line or over the phone. Look for local help.
